Unconsolidated Investments - Additional Information (Detail)
9 Months Ended 9 Months Ended
Sep. 30, 2014
Grand [Member]
Dec. 31, 2013
Grand [Member]
Sep. 30, 2014
South Kent [Member]
Dec. 31, 2013
South Kent [Member]
Jun. 25, 2014
E1 Arrayan [Member]
Dec. 31, 2013
E1 Arrayan [Member]
Schedule of Equity Method Investments [Line Items]            
Percentage of ownership 45.00% 45.00% 50.00% 50.00% 70.00% 31.50%
PPA of project 20 years   20 years